US visa for EU cruisers

[BentP]

We are having a discussion about what kind of Visa we need to enter US destinations, when we arrive in our own boat.

Will an ESTA be enough, or do we need to go to an embassy and get a visa in our passports, before we arrive?
Some say that if you want to go to say St Thomas, you have to go by ferry from an island outside US Virgins, get your visa, and only then you can enter US with your own boat.

Is this correct?

Bent/ SY Karma